Electrothermal actuator and safety devices therefor



Jan. 26, 1965 w, ZMUDA ETAL 3,166,894

ELECTROTHERMAL ACTUATOR AND SAFETY DEVICES THEREFOR Filed Dec. 9, 1963 2 Sheets-Sheet 1 I Q 37 j- 7 T. 57 f L 6 22 1TAMT L 3 W/ 53 lnl um 42 l2 I3 26 27 28 7 24 IO 6/ 34 I7 29 4/ 43 52 INVENTORS. AndrewNZmuda Sfanley Richards Marvin A. Sfaschke Jan. 26, 1965 A. w. ZMUDA ETAL 3,165,394

ELECTROTHERMAL ACTUATOR AND SAFETY DEVICES THEREFOR Filed Dec. 9, 1963 2 Sheets-Sheet 2 1 1 -4 a 29 L 9 36 43 52 I 34' rl V 23 4a 5855 Wm 4351i 46 r- Q-- 25 gi! 27 I-iai n 62 \65 5: lllllmlmvA (h y; 35 3O I0 28 H 3/ 42 maxi e5 INVENTORS'. AndrewNZmuda Stanley Richards Marvin A. Sfaschke flemidwm ATTORN Y United States Patent 3,166,894 ELECTRGTHERMAL AQTUATOR AND SAFETY DEVICES THEREFQR Andrew W. Zrnuda, Denver, and Stanley Richards and Marvin A. Staschke, Thornton, Colo., assignors to Thermal Hydraulics, Inn, Denver, Colo., a corporation of Colorado Filed Dec. 9, 1963, Ser. No. 328,978 2 Claims. (CI. 60-23) This invention relates to an electrothermal actuator and safety devices therefor. The improvement has been embodied in an electrothermal actuator of the kind shown and described in the copending application of John F. Sherwood, Serial No. 314,143, filed October 7, 1963. Such an electrothermal actuator is designed to impart motion to mechanism. It comprises a high pressure casing, a shaft reciprocably mounted in the casing having a work-actuating end portion adapted to project beyond the casing, expansible and contractible material in the casing moving the shaft in axial direction into work-actuating position, electrical switch mechanism mounted in the casing having an opening between its sides axially aligned with and adapted for passage of the shaft therethrough, and means located circumferentially on the shaft between the shaft ends for engaging and actuating said switch mechanism when the work-actuating end portion of the shaft has passed through the switch mechanism into contact with the work.

We have found that in the operation of the actuator described, injury to the switch mechanism or to the mechanism to be moved by the actuator, or both, may occur if the actuator shaft is relieved of its work-load while the actuator is operating. For example, if the actuator is being employed to operate a valve which controls a water fiow, and the flow is suddenly cut off while the actuator shaft is performing its power stroke. the unrestrained outward movement of the shaft in axial direction under influence of the pressure produced by the expansible material in the casing may cause breakage or distortion of the switch mechanism and also of the valve. If the actuator is operating a valve under a 250 pound load and the water pressure is turned off while the actuator is functioning, the actuator shaft will be forced through the switch and force the valve parts to their extreme limits, which could result in damage to the valve and to the actuator switch.

The object of our invention is to provide means in the actuator casing and on the actuator shaft for limiting the length of the power stroke of the shaft, so that the shaft is relieved of its work load while the actuator shaft is responding to pressure within the actuator casing, the power stroke is automatically terminated.

Injury to the switch mechanism also can result if the valve or other work to be contacted by the actuator shaft is not accurately positioned relatively to the end of the shaft. In such event, the shaft may advance on its power stroke beyond its predetermined stroke before encountering the work load and before being halted by actuation of the switch mechanism and opening of the switch contacts. For this purpose we have devised over-travel means hereinafter described.

The object of our invention is to provide safety devices which prevent injury to the switch mechanism and to the mechanism intended to be operated by the electrothermal actuator. This and other objects and advantages will become apparent from the drawings and following speci fication.

In the drawings:

FIG. 1 is a longitudinal vertical sectional view in the plane of the line 11 of FIG. 3, showing an electrothermal actuator embodying one of our safety devices, the

actuator shaft being shown in retracted position and switch contacts closed.

FIG. 2 is a view similar to FIG. 1, showing part of the actuator, the shaft in advanced position and switch contacts open.

FIG. 3 is an elevational end view of the actuator, with the switch housing end plate removed and the shaft in section.

FIG. 4 is a view similar to FIG. 1, showing another safety device for the actuator, the actuator shaft being in retracted position and switch contacts closed.

FIG. 5 is a view similar to FIG. 4, showing part of the actuator, with the shaft in advanced position and switch contacts open.

FIG. 6 is an exploded perspective view of part of the actuator shaft and of the safety device of FIG. 4.

Referring to FIGS. 1-3 of the drawings, the thermal actuator 10, in which we have embodied our safety devices, comprises a high pressure housing 11 which encloses a chamber 12 containing expansible and contractible material such as wax or other suitable medium for imparting motion to a shaft. An electrical heating element 13 is connected to electrodes 14 mounted in insulating seals 15 in one end 16 of the housing 11. Connected to the other end of the housing 11 is a shaft bearing housing 17 provided with bores of different diameters for having mounted therein a reciprocated shaft 20 and shaft bearing and seals. The shaft 2t comprises a piston portion 21 extending into the chamber 12 and an opposite free work portion 22 on which is mounted an elongated cap 23 having a flange 25 in its inner end and a shoulder or flange 24 near but spaced from the flange 25. The shoulder 24 may be provided conveniently by making the cylindrical wall of the cap 23 slightly thinner between the shoulder 24 and free end of the cap than between the flange 25 and shoulder 24. The flange 25 is larger in diameter than the flange 24.

The shaft 26 is mounted in a piston seal 26, lubricant bearing 27 and lubricant seal 28. Assembly of the housings 11 and 17 firmly confines the seals and shaft bearing, both axially and radially.

That portion 29 of the housing 17 adjacent the lubricant seal has a shaft receiving bore adapted to slidably receive the shaft 20, said bore being smaller in diameter than the bore 3%, thus forming a radial shoulder 31 between the bores 29 and 30 which serves as a stop for the flanged end 25 of the cap. The presence of the portion 29 of the housing between the flanged end 25 of the shaft cap and lubricant seal 28 serves to confine the seal, limits the return stroke of the shaft, and prevents the shaft cap flange from bearing on the seal 28.

The end 32 of the housing 17 is larger in diameter than the housing to form a switch chamber closed by an end plate 33. The switch chamber is proportioned to receive an electrical switch mounted concentrically with the shaft 20 and constructed to receive direct axial thrust for actuation of the switch mechanism. The housing 32 also encloses the end of the conduit 34 encasing the electrical wiring 34' between the switch and the electrodes 14.

The switch 35 comprises a fiat bottom base of insulating material, provided with a central opening 37 and peripheral recesses which accommodate the conduit 34 and mounting screws 38, 39. The base 36 is thickened by a blade supporting portion 40 located on the upper surface of the base adjacent one side of the base periphery. Concentric with the central opening 37 is a recess 41 in the top surface of the base 36.

A fixed contact support 42 with contact point 43 is fastened to the base by prongs 44. The support end opposite the point 43 is provided with a hole 45 for attachment of the electrical wiring 34'. A movable contact blade 46, as a whole, is fastened by rivets 47 to the blade supporting portion 4a of the base. Said blade 46 comprises a pair of parallel spring metal arms 48 connected together at one end by the curved cross member 49 with apertured extension Ed, and at the opposite end by the converging portions 51 of the arms carrying the depending contact point 52 at their junction. Extending inwardly from the junction of the portions 51 is a leaf spring 53. The blade 46 is mounted on the base portion ll? of the base in such position that the contact 52 registers with the fixed contact 43.

Between the base 36 and blade 43, above the recess 4-1, is a floating disc 55 of insulating material, cut away at one side 56. The disc is provided with a central aperture 57 smaller in diameter than the opening 37 in the baseand concentric with said opening. The floating disc 55 has a depending peripheralflange 58 for seating in the recess 41. The central hole 57 communicates with a slot 59 extending to the cut away side edge 56. A rib 6% extends diametrically across the top of the floating disc A retainer ear comprises a base 61 and upturned ear 62 provided with a groove 63 which extends across the face of the ear for reception of the end of the leaf spring 53. The ear base f is fastened to the switch base by rivet 54.

An upper stop comprises a base 65 with prongs 66 for fastening the stop on the base 36 in such position that the flat top member 67 overlies the arms 51 above the movable contact 52.

When the described parts are mounted on the base 35, the floating disc 55 rests loosely on the base, with the flange 58 in the base recess 41, and the apertures 37 and 57 registering concentrically. Due to the smaller diameter of the aperture 57 in the floating disc, an annular bearing surface 68 is formed on the under side of the floating disc surrounding the hole 57 for engagement by the flange 24 of the shaft cap 23 when the shaft 29 is in extended position as shown in FIG. 2.

When the switch contact points 43 and 52 are closed, as shown in FIG. 1, electrical current heats the expansible material in the chamber 12; expansion of the material causes the shaft 20 to move outwardly until the flange 24 exerts thrust in axial direction against the annular surface 68 on the floating disc 55 of the switch, as shown in FIG. 2, causing the switch blade 46 and contact point 52 thereon to separate from the fixed contact to break the circuit. Before this occurs, the shaft 29 will have reached its work-contacting position to impart motion to mechanism (not shown) located externally of the actuator.

Opening of the contacts results in cooling and contraction of the material in the high pressure chamber 12, whereupon the shaft 20 returns to the position shown in FIG. 1, for repetition of the cycle of movements. The leaf spring 53 causes closing of the contact points by snap action when the flange on the shaft cap moves away from the switch mechanism on the return stroke of the shaft. It will be understood that the return stroke of the shaft may be achieved by weight of the work on the shaft, or by a spring or other suitable means (not shown),

As pointed out hereinabove, if the shaft Zti is relieved of its work while the shaft is moving on its power stroke, the unrestrained shaft may continue its power stroke to the right of FIG. 1 after the switch mechanism has been actuated to open the contacts and before the expansion power of the material in the housing is exhausted due to cooling of the material. To avoid the possible eflects of such action, we have provided a safety device which com prises the flange 25 on the shaft 2i), screw threads 76 on beyond that intended, due to withdrawal of the workload on the shaft. The sleeve 71 may be retained in the bore 39 by means other than the threads 79 engaging the externally threaded sleeve, but the construction shown has been found eflicient for restraining and limiting the power stroke of the shaft when required as the result of unintentional or accidental removal of the work load.

Referring to FIGS. 4-6, the safety device embodied in the actuator heretofore described consists of a split flat type spring '73 which has a snug fit on the shaft cap 23 adjacent the flange or shoulder 24 on the side toward the free end of the shaft. The spring '73 actuates the switch by contacting the floating disc 55, in the same marner that the flange or shoulder 24 of the shaft cap actuates the switch of FIGS. 1-3, except that the central opening 37 in the switch base 3:; is enlarged to receive the spring 73 and the central opening 57 in the disc 55 is enlarged to allow the flange 24 to pass through it without actuating the float disc. The spring is capable of slipping over the flange 24 onto that part of the shaft cap 23 located between the flanges 24 and 25', but is prevented from slipping beyond that distance by the larger diameter flange 25 on the inner end of the cap. This is an overtravel safety feature which provides additional variablelength stroke for the shaft after the switch has been actuated so the tension on the blade 4-6 is not over-stressed and possibly damaged. This feature is employed where the mechanical stop, 7t 71, '72, of FIGS. 1-3, is dispensed with in cases where the mechanism to be actuated by the shaft 2%? is provided with its own mechanical stop. The spring 73 provides for automatic variable adjustment of the shaft stroke to compensate for minute misadjustment of the shaft end and the mechanism it is designed to contact. The pressure required to move the spring from the position of FIG. 4 to that of FIG. 5 is far less than the pressure needed to injure the switch blade 46, but greater than that needed to actuate the floating disc 55 of the switch. This over-travel feature thus eliminates the necessity for fine tolerances in the switch mechanism and relation of the shaft to the work. The diametrical dimensions of the flanges 24 and 25 on the shaft cap 23, and the construction of the shaft 20 and cap 23 are identical for use with either of the two safety devices, namely, the mechanical stop member 71, 72, of FIGS. 1-3 and the flat spring 73 of FIGS. 4-6. The safety devices are interchangeable, that is, the possessor of the actuator equipped with the capped flanged shaft described herein may utilize either of the safety devices by merely installing one or the other and selecting the appropriate switch mechanism shown in either FlGS. 1-3 for use with the mechanical stop member 71, 72, or in FIGS. 4-6 for use with the spring over-travel device 73. Changes may be made in details of construction and form and arrangement of parts without departing from the scope of the invention as defined by the appended claims.

We claim: 7 1. In an electrothermal actuator comprising a high pressure casing, a shaft reciprocably mounted in the casing having a work-actuating end portion adapted to project beyond the casing, the inner end of the shaft being a piston portion, expansible and contractible material in the casing moving the shaft in axial direction into work-actuating position, electrical switch mechanism mounted in the casing having an opening axially aligned with and adapted for passage of the shaft therethrough, and a first flange located circumferentially on the shaft between the shaft ends, the improvement which consists of a safety device providing for variable-length power stroke of the shaft, said device comprising (a) a stop flange located circumferentially on the shaft between the piston portion and said first flange, (b) a flat radially extending spring mounted on the shaft adjacent the first flange for actuating the switch mechanism when the work-actuating end por- 5 tion of the shaft has passed through the switch mechanism,

(b-l) said spring being slidable across said first flange and on the shaft between the stop flange and said first flange when the shaft has moved in axial direction beyond its predetermined power stroke.

2. The electrothermal actuator safety device defined by claim 1, in which the pressure required to move the spring across the first flange being less than the pressure which would injure the switch mechanism and greater than the pressure needed to actuate the switch mechanism.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN AN ELECTROTHERMAL ACTUATOR COMPRISING A HIGH PRESSURE CASING, A SHAFT RECIPROCABLY MOUNTED IN THE CASING HAVING A WORK-ACTUATING END PORTION ADAPTED TO PROJECT BEYOND THE CASING, THE INNER END OF THE SHAFT BEING A PISTON PORTION, EXPANSIBLE AND CONTRACTIBLE MATERIAL IN THE CASING MOVING THE SHAFT IN AXIAL DIRECTION INTO WORK-ACTUATING POSITION, ELECTRICAL SWITCH MECHANSIM MOUNTED IN THE CASING HAVING AN OPENING AXIALLY ALIGNED WITH AND ADAPTED FOR PASSAGE OF THE SHAFT THERETHROUGH, AND A FIRST FLANGE LOCATED CIRCUMFERENTIALLY ON THE SHAFT BETWEEN THE SHAFT ENDS, THE IMPROVEMENT WHICH CONSISTS OF A SAFETY DEVICE PROVIDING FOR VARIABLE-LENGTH POWER STROKE OF THE SHAFT, SAID DEVICE COMPRISING (A) A STOP FLANGE LOCATED CIRCUMFERENTIALLY ON THE SHAFT BETWEEN THE PISTON PORTION AND SAID FIRST FLANGE, (B) A FLAT RADIALLY EXTENDING SPRING MOUNTED ON THE SHAFT ADJACENT THE FIRST FLANGE FOR ACTUATING THE SWITCH MECHANISM WHEN THE WORK-ACTUATING END PORTION OF THE SHAFT HAS PASSED THROUGH THE SWITCH MECHANISM, (B-1) SAID SPRING BEING SLIDABLE ACROSS SAID FIRST FLANGE AND ON THE SHAFT BETWEEN THE STOP FLANGE AND SAID FIRST FLANGE WHEN THE SHAFT HAS MOVED IN AXIAL DIRECTION BEYOND ITS PREDETERMINED POWER STROKE. 